Characterization of a conserved outer-membrane protein in non-typeable <i>Haemophilus influenzae</i> with an unidentified impact on phenotype

Non-typeable <i>Haemophilus influenzae</i> (NTHi) is a major human pathogen for which there is no vaccine. Subunits for a rationally designed vaccine need to be conserved and present in almost all strains of an organism, be stably expressed, and be surface-located, so they will be "recognized" by the immune system. Our work sought to determine if a highly conserved NTHi protein, NTHI1101, was surface-located and required for pathobiology. Characterization showed that this protein was located in the outer membrane, but not present on the bacterial cell surface, and not required for key aspects of disease. We therefore conclude that NTHI1101 should not be further investigated as a vaccine candidate, so that ineffective antigens are not included in an NTHi vaccine.